Both of the Middleton sisters are considered style icons, but at the christening of Kate Middleton's third child, Prince Louis, on Monday, she and younger sister Pippa chose to have something else in common.

While the Duchess of Cambridge chose Alexander McQueen for the event, Pippa, 34, showed off her growing baby bump in a pastel blue dress by Alessandra Rich featuring a pleated skirt teamed with matching baby blue hat and high heels by Jimmy Choo.

Her long brunette hair was pulled back from her face and her makeup subtle.

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However if you look more closely at each of the Middleton sister's ensembles that day, you'll notice both are wearing floral stud earrings for the occasion.

Proud mum Kate is wearing pearl floral earrings for her third child's christening, while Pippa chose a more modern gold style.

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The two clearly have similar taste in fashion, with many commenting that Pippa's wedding gown at her wedding to James Matthews in May 2017 similar to Kate's iconic wedding look.

Husband James chose a matching light blue tie for the event.

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While Pippa is reportedly five months pregnant with her first child, her baby bump barely showed.

She confirmed the pregnancy last month in a fitness column called 'Exercising During Pregnancy' published in UK supermarket magazine Waitross Kitchen.

Pippa told the publication she didn't suffer morning sickness like older sister Kate who endured severe morning sickness or Hyperemesis Gravidarium during each of her three pregnancies.

"I was lucky to pass the 12-week scan without suffering from morning sickness," she said. "That meant I was able to carry on as normal."

While Pippa Middleton has been keeping a low profile since it was revealed she is expecting her first child, on Thursday at Wimbledon she and brother James were preparing to take their seats in the Royal Box on Centre Court when a side-on glimpse at Pippa revealed her growing bump.

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Pippa was one of the first guests to arrive at Prince Louis' christening at St James' Palace in London.

The proud aunt is said to have a special bond with her youngest nephew and was the first person to meet him after Kate gave birth earlier this year.

Their children are expected to be very close, just as close as the sisters are to each other.